Train speed control system



June 10, 1958 c. s. WILCOX TRAIN SPEED CONTROL SYSTEM Filed June 17, 1955 INVENTOR. C. S W LC 0X EMW HIS ATTORNEY United States Patent 2,838,657 I TRAIN SPEED CONTROL SYSTEM Clinton S. Wilcox, Brighton, N. Y., assignor to General Railway Signal Company, Rochester, N. Y.

Application June 17, 1955, Serial No. 516,067

2 Claims. (Cl. 246-182) This invention relates to speed control systems for vehicles, and more particularly pertains to frequency responsive electronic apparatus using transistors in a control system for regulating the speeds of trains.

Railroad locomotives are frequently equipped with a mechanical, axle-driven, centrifugally operated speed contactor. This contactor has one or more contacts that close at respective predetermined speeds and may be used with associated apparatus to limit the speed of the train. However, since the speed contactor is mounted on the journal box of the locomotive or tender, it is subject to severe vibrations that tend to affect its reliability To overcome this inherent difiiculty with respect to the mechanical type of contactor, a speed responsive circuit contactor was developed comprising an axle-driven frequency generator whose output frequency is proportional to train speed. The output of this frequency generatoris fed over a cable to electronic apparatus at a remote location on the locomotive. This variable frequency signal is applied to an electron tube amplifier and associated filtering means, and the resulting output is used to control a brake controlling electropneumatic valve. When the train speed exceeds a'predetermined maximum desired value, the output frequency of the frequency generator becomes sufficiently high to be passed by the filtering means and cause actuation of the valve if the brakes are not promptly applied by the trainman. If actuation of this valve occurs, however, an automatic brake application follows.

In the speed control system of this invention, the variable frequency signal obtained from the frequency generator is applied through a high-pass filter to an improved amplifier organization comprising a plurality of transistor amplifier stages. When the train is operating below its preselected maximum speed, the output frequency of the frequency generator is blocked by a highpass filter. Under these conditions, an electromagnetic relay controlled by the final stage of the transistor amplifier is energized. While it is thus energized, this relay is able to maintain the electro-pneumatic brake-controlling valve continually energized. However, when the preselected maximum speed of the locomotive is reached, the output frequency of the frequency generator becomes sufficiently high to pass through the high-pass filter. The electromagnetic relay then becomes deenergized with the result that the electro-pneumatic valve then also becomes deenergized to provide an automatic brake application unlessa service brake application is promptly made by the trainman An object of this invention is to provide a speed control system for trains wherein a variable frequency, proportional to the speed of a train, is amplified by an improved transistor amplifier.

' Another object of this invention is to provide a speed control system for trains comprising a transistor amplifier havingimproved temperature compensation characteristics. l

Other objects, purposes, and characteristic features of this invention will in part be obvious from the accompanying drawings and in part pointed out as the description of the invention progresses.

In describing this invention in detail, reference will be made to the accompanying drawing which illustrates in detail one embodiment of this invention.

To simplify the illustration and facilitate the explanation of this invention, the various parts and circuits have been shown diagrammatically. Certain conventionalillustrations have been employed, and the drawing has been made to make it more easy to understand the principles and manner of operation rather than to illustrate the specific construction and arrangement of parts that might be used in practice. The various relays and their contacts are illustrated in a conventional manner and symbols are used to indicate connections to the terminals of batteries or other sources of electrical current instead of showing all the wiring connections to these terminals. Thus, the symbols and indicate the opposite terminals of a suitable source of direct current power used for operation of both the relays and the transistors.

The vehicle-carried axle-driven frequency generator which provides an output frequency proportional to the train speed is shown diagrammatically in the drawing. Described briefly, this frequency generator comprises a toothed tone wheel operating in a magnetic circuit and causing a voltage to appear by induction in the winding 11. This frequency generator may assume any of various forms and may be of the kind shown in the patent to O. S. Field, No. 2,651,734, dated September 8, 1953. One terminal of the winding 11 is connected over Wire 12 to the input terminals of a high-pass filter 13, and the other terminal of winding 11 is connected to a wire 14. The high-pass filter 13 is organized to attenuate sharply the lower frequencies corresponding to vehicle speeds below the preselected maximum value. It is only when the vehicle speed exceeds this preselected value that the filter passes the frequency induced in winding 11 so that an output voltage can appear between wires 14 and 15;

' The various transistors shown are all assumed to be of the p-n-p junction type. Other kinds of transistors may equally well be used provided that, where required, the bias connections are altered to provide the proper polarities for correct operation of the various stages.

' The first stage of the amplifier comprises the transistor 16 which is connected to operate as a grounded collector stage. A grounded collector stage has a high input impedance and a low output impedance. Such a stage is; therefore. particularly useful in matching the high output impedance of the filter 13 to the low input impedance of the grounded base transistor stage including transistor 17.

The output signal passed by the filter 13 when train speed exceeds the preselected value is applied through a coupling capacitor 18 to the base of transistor 16. The collector of this transistor is connected directly to the common wire 14. The base is connected through resistor 19 to the junction of resistors 20 and 21 connected in series across the battery 22. The emitter is connected through resistor 23 to wire 24 which is connected directly to the positive terminal of battery 22. The proper bias potentials for the transistor 16 are thus provided, i. e. the emitter, connected to the terminal through resistor 23, is positive with respect to the base which is at a potential between that of the and ,terminals, while the collector is maintained at a negative potential with respect to the voltage on the base.

The output signal of transistor 16 is obtained from its emitter and passed through coupling capacitor 25 to the emitter of voltage amplifier transistor 17. The base of this transistor is connected over wire 24v to terminal of battery 22. Since the emitter of this transistor is connected through resistor 26 also to this wire 24, there is normally no bias voltage presentbetween emitter and base so that this transistor is normally cut off when .no signal is present.

The collector of transistor 17 is connected through resistor 27 and capacitor 28 in parallel to a tap on potentiometer 29 which is connected directly across the battery 22. The position of this tap on potentiometer 29 provides a voltage at the lower terminal of resistor 27 that is appreciably negative with respect to that appearing on wire 24. The emitter of the relay control transistor 31 is connected to the junction of resistors 32 and 33 connected in series between the tap 34 on potentiometer 29 and the terminal of battery 22. The base of transistor 31 is connected through resistor 35 to this tap 34 also.

When transistor 17 is in its normal cutoif condition so that there is minimum current flow through resistor 27, the voltage at the collector is very nearly equal to the negative voltage on the lower terminal of resistor 27. At such time, the voltage applied through resistor 30 to the base of transistor 31 causes this point to be negative with respect to the emitter. It has been found that with transistor 17 cut off, the base of transistor 31 is a few tenths of a volt negative with respect to the emitter, and this causes transistor 31 to be conductive so that a current passes through the winding of relay R and causes this relay to be normally energized.

When the train speed reaches a sufficiently high value so that an output signal appears between wires 14 and 15, the alternating-current signal is amplified by transistor 16 and passed through capacitor 25 to appear between the emitter and base of transistor 17. Since this transistor is normally biased to cutoff, it conducts on the positive half-cycles ofthe input signal, causing current to flow at such time in the collector-base circuit. There is then a voltage drop through resistor 27 that causes the collector voltage to rise to a value nearly equal to that appearing on wire 24. Capacitor 28, incidentally, provides a filtering action and is effective to reduce the ripple voltage appearing in the collector circuit. The reduction of collector voltage of transistor 17 produces a substantial reduction in the negative voltage present at the base of transistor 31. In one embodiment of this invention, for example, it was found that the change in the condition of, transistor 17 from a cutoff to a conductive condition caused the voltage at the base of transistor 31- to vary from l3 to approximately volts. This is accompanied by a change in the voltage at the emitter also,

but this change is of a substantially smaller amount. Thus, in the embodiment mentioned, the emitter voltage varied from l2.5 volts to 9.5 volts. Consequently, whereas the base was before slightly negative with respect to the emitter, it is now several volts positive so that the transistor 31 is fully cutoff. As a result, relay R is deprived of energizing current and drops away.

In general, the collector current of a transistor tends to increase with an increase of temperature. This condition makes itmore difficult to fully cut off a transistor when high ambient temperatures prevail. A failure to cut off transistor 31 when the generated frequency is passed by filter 13 results in the improper energization of the winding of relay R. If this current should reach suificient amplitude to cause this relay to pick up, the overspeed control would become entirely ineffective. To prevent this, the bias power supply is so organized and connected to the various transistor elements that the output transistor 31 is assured of being fully cut off whenever transistor 17 is conductive, i. e. whenever train speed exceeds the predetermined value.

To accomplish this function, several different voltage levels are provided by shunting the battery22 with a 4: I potentiometer 29 having a plurality of taps. The collectorbase voltage of transistor 17 is obtained from the voltage existing between the terminal of battery 22 and tap 36 on potentiometer. The base of transistor 31, on the other hand, may be considered as being connected to a tap on a voltage divider comprising resistors 27, 30 and 35 connected in series between taps 36 and 34 of potentiometer 29.

When transistor 17 becomes conductive so that its collector voltage becomes appreciably less negative, the voltage at the base of transistor 31 also assumes a less negative value. At such time, transistor 31 should be cutoff, but this can be assured of happening under high temperature conditions only by making the emitter substantially negative with respect to the base so as to prevent any current flow. This condition is conveniently provided in the present invention, since the use of the tapped potentiometer 29 makes it possible to connect the emitter to the junction of resistors 33 and 32 connected in series between the terminal of battery 22 and tap 34 of potentiometer 29. The emitter voltage thus readily is made more negative by a substantial amount than the voltage present at the base under cutoff conditions, thereby ensuring that no current can flow in the Winding of relay R when train speed exceeds the predetermined value.

From the description that has been given, it is evident that relay R is normally in a picked up condition whenever the system is in operation, and that this relay drops away only when the train speed reaches such a value that the frequency of the voltage induced in winding 11 is passed by the high pass filter 13.

Whenever relay R is picked up, a circuit is completed from the terminal of battery 22, through front contact 37 of relay R and the winding of relay C, to the terminal of battery 22. This circuit causes relay C also to be normally energized so that a circuit can then be completed through a front contact 38 of relay C to energize the electro-pneumatic valve EPV by current obtained also from battery 22. Under these conditions, the front contact 39 of relay R is also closed so that the whistle valve WV is continually energized. This energization of the whistle valve WV prevents its sounding.

When relay R drops away, its front contact 37 opens so that the winding of relay C becomes deenergized. At the same time, front contact 39 of relay R is opened, thereby deenergizing the whistle valve WV. The sounding of the whistle, that then occurs provides an audible warning to the trainman that the train speed limit has been exceeded so that relay R has been dropped away. Since the relay C is provided with slow releasing characteristics, as indicated 'by the heavy base line for the symbol representing this relay, it does not immediately drop away upon the openingof front contact 37. If the trainman is alert and promptly provides a service brake application, the contacts 40 of the suppression contactor SC will close and provide a stick circuit through these contacts 40 and front stick contact'41 of relay C to hold relay C ina picked-up condition. 'More specifically, if the brakesare promptly applied by the trainman, an increase of pressure will occur at the inlet pipe 42 to the suppression contactor SC. The piston 43 will then move in the cylinder 44 against the compression, of the spring 45 so as to close the contacts 40. Various kinds of suppression contactors may be used for this purpose. One such contactor is disclosed in the patent to C. S. Bushnell No. 1,757,410, dated May 6, 1930.

If, however, the service brake application is not made i so as to close contacts 40 in the interval between the opening of front contact 37 and the dropping away of relay C, the relay C will drop away and open its front contact 41 so that it can then no longer be held energized through the contacts 40. When relay C does drop away, its front contact 38 is opened so that the electro-pheumatic valve EPV is deenergized. This deenergization of the valve provides an automatic application of the brakes. Relay C can then again become energized only when train speed has been sufiiciently reduced by the brake applica tion to result in the picking up of relay R and the closure of front contact 37.

Having described an improved train speed control system using transistor circuits as one specific embodiment of this invention, I desire it to be understood that various modifications, adaptations, and alterations may be made to the specific form shown to meet the requirements of practice Without in any manner departing from the spirit or scope of this invention.

What I claim is:

1. In a speed control system for trains, an axle-driven frequency generator having a coil with a voltage induced therein proportional in frequency to the speed of said train, filtering circuit means having said voltage applied thereto and providing an output only When said frequency exceeds a predetermined value, transistor amplifier circuit means for amplifying the output of said filtering circuit means and comprising, a biasing direct-current power source shunted by a multiple tapped potentiometer to provide voltage levels intermediate between those provided by said source, a grounded base transitor voltage amplifier having its base and emitter connected to one terminal of said source, said voltage amplifier transistor having its collector connected through a load impedance to one of said taps on said potentiometer, a grounded emitter transistor relay control amplifier, said collector of said voltage amplifier transistor being connected through a resistor to the base of said relay control amplifier transistor, said base of said relay control amplifier transistor being connected through a resistor to another tap on said potentiometer, said emitter of said relay control amplifier transistor being connected to the junction of two resistors connected in series between said another tap on said potentiometer and the other terminal of said source, an overspeed relay having its winding connected between said collector of said relay control amplifier transistor and said other terminal of said source, said voltage amplifier transistor upon being rendered conductive by the output of said filtering circuit means being effective to cut ofi said relay control amplifier transistor by a substantial margin to thereby ensure that'said overspeed relay is fully deenergized irrespective of ambient temperature, and circuit means responsive to the dropping away of said relay for controlling the speed of said train.

2. In a speed control system for trains, an axle-driven generator having a coil with a voltage induced therein proportional in frequency to the speed of such train, filtering circuit means having said voltage applied thereto and providing an output current only when said frequency exceeds a predetermined value, transistor amplifier circuit means for amplifying the output of said filtering circuit means and comprising, a biasing directcurrent source shunted by a multiple tap potentiometer to provide voltage levels intermediate between those provided by said source, a voltage amplifier including a grounded base transistor of the p-n-p junction type having its base and emitter connected to the positive terminal of said source, said voltage amplifier transistor having its connector connected through a load impedance to one of said taps on said potentiometer, a relay control amplifier including a grounded emitter transistor of the p-n-p junction type, said collector of said voltage amplifier transistor being connected through a resistor to the base of said relay control amplifier transistor, said base of said relay control amplifier transistor being connected through a resistor to another tap on said potentiometer providing a voltage more positive than that provided by said one tap, said emitter of said relay control amplifier transistor being connected to the junction of two resistors in series between said more positive tap and the negative terminal of said source, an overspeed relay having its winding connected between said collector of said relay control amplifier transistor and said negative terminal of said source, said voltage amplifier transistor upon being rendered conductive by the output of said filtering circuit means being efiective to cut ofi said relay control amplifier transistor by a substantial margin to thereby ensure that said overspeed relay is fully deenergized irrespective of ambient temperature, and circuit means responsive to the dropping away of said relay for controlling the speed of said train.

References Cited in the file of this patent UNITED STATES PATENTS 2,585,078 Barney Feb. 12, 1952 2,653,282 Darling Sept. 22, 1953 2,698,416 Sherr Dec. 28, 1954 2,719,911 Maenpaa Oct. 4, 1955 2,719,912 Maenpaa Oct. 4, 1955 2,721,258 Freehafer Oct. 18, 1955 2,730,576 Caruthers Jan. 10, 1956 

